A069832 Prefixing, suffixing or inserting a 7 in the number anywhere gives a prime.

1, 3, 9, 19, 27, 33, 39, 57, 87, 97, 159, 177, 187, 433, 487, 541, 603, 691, 717, 753, 757, 853, 949, 1257, 1471, 1707, 2277, 2367, 2617, 2953, 4317, 4507, 4623, 4779, 4797, 5773, 6481, 6757, 6777, 7017, 7351, 7417, 7471, 7479, 7747, 7797, 7813, 7977

Offset

1,2

Links

Giovanni Resta, Table of n, a(n) for n = 1..2399 (terms < 10^13, first 201 terms from Harvey P. Dale)

Mathematica

psi7Q[n_]:=Module[{idn=IntegerDigits[n]}, And@@PrimeQ[FromDigits/@ Table[ Insert[ idn, 7, i], {i, Length[idn]+1}]]]; Select[Range[8000], psi7Q] (* Harvey P. Dale, Sep 18 2012 *)

Crossrefs

Cf. A068674, A068679, A069833.

Sequence in context: A056682 A032670 A068677 * A057257 A029464 A029479

Adjacent sequences: A069829 A069830 A069831 * A069833 A069834 A069835

Keyword

base,nonn

Author

Amarnath Murthy, Apr 14 2002

Extensions

More terms from Vladeta Jovovic, Apr 16 2002

Offset changed to 1 by Giovanni Resta, Oct 14 2019

Status

approved